1. Field of the Invention
This invention relates to a method of constructing a modular bridge across a span and to a vehicle for use in such a method.
In military operations, it is desirable, if not essential, to have a capability for allowing heavy ground equipment, such as tanks, to cross difficulties in terrain. Such difficulties may include gaps formed by ditches, canals and rivers. Although the construction of a bridge for light vehicles is comparatively straightforward, providing a bridge which is capable of supporting a tank is of considerably greater difficulty.
2. Information Disclosure Statement
EP-A-No. 0081388 discloses a modular bridge comprising at least one intermediate bridge module and two end bridge modules, each of the bridge modules comprising two longitudinal main girder structures and an intermediate deck having a deck surface, the main girder structures being foldably connected one along each side of the deck and being foldable from an operative position in which the main girder structures offer extensions of the deck surface on either side of the deck for use to a closed position in which the main girder structures are folded beneath the deck, the main girder sturctures of the end bridge modules being longitudinally tapered in depth when seen from a side of the module in its operative position, the main girder structures of the intermediate module(s) not being so tapered, wherein each of the end bridge modules and the intermediate bridge module(s), are connected to form a bridge.
EP-A-No. 0081388 discloses the construction of such bridge by putting up a building frame, having upwardly facing rollers, on the first bank of the span to be crossed. A preliminary beam is assembled on the frame and pushed outwards towards the bank. The bridge aseembly is assembled progressively on the frame, behind the preliminary beam, with the beam being attached to the leading module. The preliminary beam has at its outer end a jacking unit with support rollers so that, when the jacking unit reaches the far bank of the span, it may rest on its and allow the assembly of beam and bridge to roll across the span, the bridge assembly is then lowered onto the bank and the beam withdrawn back through the bridge assembly. This procedure is illustrated in FIGS. 23A to 23F of EP-A-No. 0081388.
EP-A-No. 0075671 discloses a demountable non-opening bridge comprising discrete channel-section modules and an H-section launching girder, wherein modules comprise a central part and two wing parts, the wing parts comprise box-section track girders, the two wing parts are downwardly hinging below the central part for transportation, in the laying of the bridge the launching girders are assembled and made first, whereafter the various modules are coupled together and pushed over the launching girder and the launching girder remains in the bridge as a bearing element.
EP-A-No. 0075671 discloses the construction of such a bridge by the joint use of a laying vehicle having a cantilever arm and a four-tonne crane. The laying vehicle moves to the bank of the span to be crossed with a launching girder ramp (or end) member already in position on guide rollers of the cantilever arm. The cantilever arm comprises a pinion to advance the ramp member over the span by means of a cooperating rack. The crane delivers launching girder inner sections which are coupled up and advanced. Once the launching girder has reached the required length, a second launching girder ramp (end) member is coupled up. The cantilever arm of the laying vehicle is lowered so that the launching girder is then supported by its own hydraulically deployable feet. A ramp (end) bridge module is now lifted by the crane onto the launching girder. Inner (intermediate) bridge modules are coupled up and drawn over the launching girder by means of a block and tackle and reversing roller. The final module is a further ramp (end) module. The hydraulic feet are than retracted. This construction sequence is as illustrated in FIG. 6 of EP-A-No. 0075671.
EP-A-No. 0075671 also discloses the use of a single laying vehicle combining the capabilities of the laying vehicle and crane described above. It is equipped both with a cantilever arm and with a four-tonne crane.
The bridge construction procedures disclosed in EP-A-No. 0075671 involve the launching rail, once completed, being removed from the launching vehicle before any of the bridge modules are positioned on the launching rail. Since successive bridge modules will be coupled together on the launching rail in position over the span, it is not a particularly simple (or, therefore, quick) exercise to couple succesive modules together. It is to be appreciated that military modular bridges are to be capable of being built quickly, even at night, by few men.